wagmi

npm install wagmi viem @tanstack/react-query
npm install @rainbow-me/rainbowkit    # optional: beautiful wallet modal

// lib/wagmi.ts — wagmi configuration
import { createConfig, http } from 'wagmi'
import { mainnet, polygon, arbitrum } from 'wagmi/chains'
import { injected, walletConnect } from 'wagmi/connectors'

export const config = createConfig({
  chains: [mainnet, polygon, arbitrum],
  connectors: [
    injected(),    // MetaMask, Coinbase Wallet, etc.
    walletConnect({ projectId: process.env.NEXT_PUBLIC_WC_PROJECT_ID! }),
  ],
  transports: {
    [mainnet.id]: http('https://eth-mainnet.g.alchemy.com/v2/KEY'),
    [polygon.id]: http('https://polygon-mainnet.g.alchemy.com/v2/KEY'),
    [arbitrum.id]: http('https://arb-mainnet.g.alchemy.com/v2/KEY'),
  },
})

// app/providers.tsx — Wrap app with wagmi providers
'use client'
import { WagmiProvider } from 'wagmi'
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
import { config } from '@/lib/wagmi'

const queryClient = new QueryClient()

export function Providers({ children }) {
  return (
    <WagmiProvider config={config}>
      <QueryClientProvider client={queryClient}>
        {children}
      </QueryClientProvider>
    </WagmiProvider>
  )
}

// components/ConnectButton.tsx — Wallet connection
import { useAccount, useConnect, useDisconnect } from 'wagmi'

export function ConnectButton() {
  const { address, isConnected } = useAccount()
  const { connect, connectors } = useConnect()
  const { disconnect } = useDisconnect()

  if (isConnected) {
    return (
      <div>
        <p>{address?.slice(0, 6)}...{address?.slice(-4)}</p>
        <button onClick={() => disconnect()}>Disconnect</button>
      </div>
    )
  }

  return (
    <div>
      {connectors.map(connector => (
        <button key={connector.id} onClick={() => connect({ connector })}>
          Connect {connector.name}
        </button>
      ))}
    </div>
  )
}

// components/TokenBalance.tsx — Read contract data
import { useReadContract, useWriteContract, useWaitForTransactionReceipt } from 'wagmi'
import { erc20Abi, parseUnits } from 'viem'

function TokenBalance({ tokenAddress, userAddress }) {
  const { data: balance } = useReadContract({
    address: tokenAddress,
    abi: erc20Abi,
    functionName: 'balanceOf',
    args: [userAddress],
  })
  return <p>Balance: {balance?.toString()}</p>
}

function TransferButton({ tokenAddress, to, amount }) {
  const { writeContract, data: hash } = useWriteContract()
  const { isLoading, isSuccess } = useWaitForTransactionReceipt({ hash })

  return (
    <button
      onClick={() => writeContract({
        address: tokenAddress,
        abi: erc20Abi,
        functionName: 'transfer',
        args: [to, parseUnits(amount, 6)],
      })}
      disabled={isLoading}
    >
      {isLoading ? 'Confirming...' : isSuccess ? 'Sent!' : 'Transfer'}
    </button>
  )
}